THE INFLUENCE OF SOIL TYPE AND TILLAGE SYSTEM ON SELECTED HERBICIDES FATE

Ing. Štefan TÓTH, PhD., Ing. Martin DANILOVIČ, PhD.
Slovak Centre of Agricultural Research – Institute of Agroecology
Špitalska 1273, 071 01 Michalovce, Slovak Republic

Lot of original scientific works deals with the herbicides fate depending up tillage practice (1, 2, 3, 4, 5). The tillage affects the soil environment strongly, so it is allowed to be a factor influencing the herbicidal fate strongly. Despite of mentioned investigation general enclosures formulation is difficult, by reason that there were exist various ways of tillage and heterogeneity of trials conditions (4). More studies have documented soil characteristics such as organic carbon (6), pH (7), texture (8), nutrient content (9), soil moisture (10), microbial population (11) and theirs impact on herbicide interaction with soil. Several long-term studies documented the great importance of climatic factors such as temperature and humidity (4). Several studies evaluate effect of farming practice on herbicide fate (12,13 and another) at which number of works dealt with annual observation (e.g. 14, 15). The effect of weather conditions and particular farming practice result in local unique fate of herbicides, including the effect of herbucides residues on cultivated crops (16). There is a few studies of herbicidal fate in conditions of Central Europe (14, 15), eventually there is no studies of impact of tillage, despite of large effort devoted to study of herbicides behaviour.

Material and methods

The field experiment with five herbicides (terbuthylazine, dicamba, metribuzin, S-metolachlor and acetochlor) was carried out at two localities, resp. at two soil types at East Slovak Lowland. Herbicides fate were observing at tree variants of soil tillage and were evaluating in two soil layers. The trial at locality Milhostov (Gleyic Fluvisol – GF) was established during the years 2005 – 2007 and the trial at lokality Vysoká nad Uhom (Eutric Fluvisol – EF) was established just one year (2005).
The list of observed factors are presented in the next table.

Table  Observed factors 
Factor	Factor level	
Soil type  - locality	Gleyic Fluvisol (GF) – locality Milhostov	
	Eutric Fluvisol (EF) – locality Vysoká nad Uhom 	
Soil tillage	No–till (NT) - direct sowing by special drill machines Great Plains and Kinnze 2000	
	Reduced tillage (RT) - shallow soil cultivation, pressowing harrowing, sowing by drill machines Great Plains and Kinnze 2000	
	Conventional tillage (CT) - stubble breaking + deep ploughing, presowing harrowing, sowing by drill machines Great Plains and Kinnze 2000	
Herbicide (crop)	at Gleyic Fluvisol: terbuthylazine (maize), dicamba (spring barley), metribuzin (soya), S-metolachlor (field bean), acetochlor (sunflower)	
	at Eutric Fluvisol: terbuthylazine (maize), dicamba (spring barley), metribuzin (soya), S-metolachlor (field pea), acetochlor (sunflower)	
Soil layer	topsoil (top.): 0.05 – 0.30 m 	
	subsoil (sub.): 0.50 – 0.60 m 	

The field trials is established by the block method. There is 10 blocks, resp. 10 plots of crop rotation (10 crop rotation). Three variants of tillage are established at each block and variants are repeated four times. Herbicidal experiment was establishing just at 5 blocks (crops). Block area is 1.5 ha and area of herbicidal variant was 56 m2 (8 x 7 m). 
Tested herbicides were applied to soil surface without incorporation, eventually foliar application was used in some cases. Herbicides were applied at registered doses and water volume was 300 l.ha-1. Herbicides doses, date of application as well as details of high detection parameters of residual analyses are presented in the table I. Other ecological parameters of herbicides are shown in table II. Soil samples were sampled at the end of  September till early in Okctober.

Tab. I. Herbicide doses, date of application and details of high detection parameters of residual analyses
Trademark / active compound (% of  trademark)	Dose
[kg, resp. l ha-1 ]	2005	2006	2007	Analytical method / detector / kv. l. / det. l.	
		GF	EF	GF	GF		
Trophy / 
acetochlor (76.8)	2.5 	10 May	9 May	12 May	20 April	GC / MS / 0.016	
Dual Gold 960 EC / S-metolachlor (96.0)	1.4 	14 April	14 April	24 April	16 March	GC / ECD / 0.01 / 0.008	
Sencor 70 WP / metribuzin (70.0)	1 	10 May	10 May	4 May	24 April	GC / ECD / 0.005 / 0.002	
Click 500 / terbuthylazine (50.0)	3	10 May	9 May	12 May	23 April	GC / ECD / 0.005 / 0.002	
Banvel 480 S  / dicamba (48.0)	0.125 	8 June	15 June	12 May	23 April	HPLC / DAD / 0.01 / 0.009	
GC – gas chromatography, HPLC – high- performance liquid chromatograph, MS – mass detector, ECD – electron capture detector, DAD – diode array detector, kv. l. – limit of kvantification, det. l. – limit of detection

Tab. II. Selected ecological parameters of active compounds (17, 18)
Active compound	Vapour pressure
[mPa ]	Water solubility at 20°C
[mg l-1 ]	Half-time period of decomposiotion  in soil DT50 [days]	Groundwater ubility score [GUS]	Absorption coefficient
[mg g-1 ]	
acetochlor	400	223	14 (13)	1.94	203	
S-metolachlor	3.7	480	22 (21)	0.76	2261	
metribuzin	0.121	1165	19 (40)	2.57	37.9	
terbuthylazine	0.15	8.5	46 (45)	2.74	220	
dicamba	1.67	5500	14 (12)	3.31	13	

 Results 

According to the measured herbicide residues content (tab. III.) there were significant differences among the solved soil types, the tillage systems, the soil layers as well as herbicides themself. However acetochlor and S-metolachlor negative all findings being meant no possiblity of statistical valuation, their remained causality can be objected. The valuation of dicamba, metribuzin and terbuthylazine is more difficult.
We had been observing two soil types in the year 2005 and one soil type in the year 2006 and 2007. There was a great difference of temperature and precipitation between the years. Weather conditions were abnormal, mainly in 2005 and 2007. Weather conditions were abnormal and heavy simulative but make harder interpretation of results.

Trail in  2005

In the preface it is necessary to note an environmental impact. On both localities untill the fifth day after application of  acetochlor, metribuzin, S-metolachlor and terbuthylazine there was no day with rain over 3.6 mm. Concerning the application of dicamba the great amount of precipitations 36.8 mm (9 June) and 12.4 mm (10 June) occured immediately a day after, that caused a  deluge and subsequently run-off at heavy clay Gleyic Fluvisol. Similarly 39.5 mm (9 June), respectively next 8.8 mm (10 June) of precipitations fallen without any deluge effect at sandy loam medium Eutric Fluvisol where the dicamba application was made in a week after the storm rainfall event when conditions were optimal. 
Consequently with the mentioned environmental event the fate of dicamba was influenced by deluge at GF. We measured less dicamba residues at heavy clay soil in comparison to sandy loam medium soil, in contradictiory with metribuzin and terbuthylazine residues. There were measured more metribuzin and terbuthylazine residues at Gleyic Fluvisol in comparison to Eutric Fluvisol. The higher metribuzin and terbuthylazine content at clay heavy soil corresponds to the herbicide higher organic carbon sorption constant in one breath with higher sorption capacity of GF as EF. There is higher sorption capacity at clay heavy soil than at sandy loam medium soil, as well as stronger terbuthylazine than metribuzin sorption potential. 
In general the dicamba, metribuzin and terbuthylazine residues content was on regularly higher level at topsoil in comparison to followed subsoil layer, however in the case of metribuzin and terbuthylazine there were no differences at EF followed soil layers. The higher terbuthylazine than metribuzin residues content at GF subsoil corresponding to  leaching potential of herbicide. The less dicamba residues content at GF, including both followed topsoil and subsoil layer, then at EF ones can be partially the result of the run-off effect caused by deluge. Among solved herbicides dicamba there are more leachingable, that agrees with its the highest subsoil residue values at EF. 
The valuation of dicamba, metribuzin and terbuthylazine residues according to the tillage system brings no uniformal effect of the used agrotechnique single impact or interaction impact of the agrotechnique on followed soil types. Concerning the tillage systems impact it is remarkable the fact that at the soil sampling we exlude the upper topsoil (0-5 cm) that include crop residues on soil surface. In the case of dicamba there was the highest residue amount at a conventionall tillage, less at no-till technology and the least at reduced agrotechnique in general. This general trend was valid for EF, but at GF the position of the conventional tillage and no-till technology was changed. The status of dicamba residues founded at Gleyic Fluvisol is probably secondary, result of deluge. Higher amounts of dicamba residues at notillage as at conventional tillage fonded at GF, were probably caused by precipitations one day after herbicide aplication. On the contrary, content of residues founded at EF was higher at convetional tillage as at notillage. There were no precipitations several day after dicamba aplication.
In the case of metribuzin and terbuthylazine residues valuation according to the tillage systems it is notable that at the EF it was only one measurable content, i.e. terbuthylazine in the topsoil at no-tillage. That fact is completely conformable with higher organic carbon sorption constant of terbuthylazine in comparison to metribuzine´s one and by the same way with the lower activity of processes of organica matter mineralisation axpected at NT.
	The status of metribuzin and terbuthylazine residues content at GF topsoil and subsoil according to the observed tillage systems were similar to each other, and probably were affected by above mentioned deluge occurred approximately a month after these herbicides application. Lower content and distribution of residues of metribuzin than terbuthylazine correlates with shorter half-life period of metribuzine in contrariety to higher half-life period of terbuthylazine. The mobility of terbuthylazine is higher despite of higher sorption potencial and correlates with longer persistzance.

Tab. III. The herbicides residues content in soil according  to soil type and variants of tillage system and soil layer
Year	Soil type	Tillage	Soil layer	Residue content in the soil [mg kg-1]	
				acetochlor	dicamba	metribuzin	S-metolachlor	terbuthylazine	
2005	GF	CT	 top. 	< 0.016 	0.250 	0.003 	< 0.008 	0.010 	
			 sub.	< 0.016 	0.070 	< 0.002	< 0.008 	0.005 	
		RT	 top. 	< 0.016 	0.160 	0.003 	< 0.008 	0.023 	
			 sub.	< 0.016 	< 0.010	< 0.002	< 0.008 	0.010 	
		NT	 top. 	< 0.016 	0.645 	< 0.002	< 0.008 	0.006 	
			 sub.	< 0.016 	< 0.010	< 0.002	< 0.008 	0.007 	
	EF	CT	 top. 	< 0.016 	0.950 	< 0.002	< 0.008 	< 0.002 	
			 sub.	< 0.016 	0.200 	< 0.002	< 0.008 	< 0.002 	
		RA	 top. 	< 0.016 	0.300 	< 0.002	< 0.008 	< 0.002 	
			 sub.	< 0.016 	0.025 	< 0.002	< 0.008 	< 0.002	
		NT	 top. 	< 0.016 	0.300 	< 0.002	< 0.008 	0.008 	
			 sub.	< 0.016 	0.035 	< 0.002	< 0.008 	< 0.002 	
2006	GF	CT	 top. 	< 0.016 	< 0.009	0.003 	< 0.008 	0.051	
			 sub.	< 0.016 	0.993 	< 0.002	< 0.008 	0.014	
		RT	 top. 	< 0.016 	0.045 	< 0.002	< 0.008 	0.056 	
			 sub.	< 0.016 	0.206	< 0.002	< 0.008 	0.009 	
		NT	 top. 	< 0.016 	0.023 	< 0.002	< 0.008 	0.018	
			 sub.	< 0.016 	0.165	< 0.002	< 0.008 	0.003 	
2007	GF	CT	 top. 	< 0.016 	< 0.009	< 0.002	< 0.008 	0.038	
			 sub.	< 0.016 	< 0.009	< 0.002	< 0.008 	0.009	
		RT	 top. 	< 0.016 	< 0.009	0.006 	< 0.008 	0.048 	
			 sub.	< 0.016 	< 0.009	< 0.002	< 0.008 	0.009 	
		NT	 top. 	< 0.016 	< 0.009	< 0.002	< 0.008 	0.005 	
			 sub.	< 0.016 	< 0.009	< 0.002	< 0.008 	0.002 	

Trial in 2006 and 2007

We present that precipitations were under the 4.6 mm during 5 days after application of herbicides in the year 2006 and 2007, except metribuzin in 2006. It was raining (6.8 mm) one day after metribuzin aplication in 2006. Average year temperatures showed that both years were above the average. Wet character had most of months in 2006, besides dry august, while the year 2007 was arid, except for September. When we ignore weather in September 2007 (very high amount of precipitation) we can state according to hydrotermic coefficient that year 2007 was abnormally arid. Precipitation had storm character in September 2007, it was raining in three rates for a period of four days (43.5 mm – 4th September, 20.7 mm – 5th September, 15.4 – 17th September and 21.2 mm –  27th September).
Residue analyses of acetochlor and S-metolachlor were negative in years 2006 and 2007 analogous to 2005. There was found similar phenomenon in case of metribuzin in the year 2006 and 2007. Measurable content of residues of metribuzin were found at the top layer of soil at reduced tillage in both mentioned years. Average content was near by detection limit in the year 2006, while the content was three times higher in the year 2007. Metribuzin was not detected at notillage and conventional tillage in both soil depths.
In the event of dicamba herbicide we found higher values of residues in the soil in the year 2006 than in the year 2005, whereas most of soil samples were negative in the year 2007. Interesting investigation is, that higher values of residues of dicamba herbicide were detected in subsoil than in topsoil in 2006. It is keeping with the highest mobility of dicamba in comparison with others tested herbicides. The reason why we did not found of dicamba residues in 2007 is fact, that herbicide was aplicated 45 day earlier than in the year 2005, and also particularity of heavy soil – preference flow by the soil cracks especialy in the year 2007.
In the event of terbuthylazine we detected higher values of residues in the year 2006 compare with 2007, it was found in the topsoil and subsoil too. Detected content of residues of terbuthylazine in 2006 and 2007 exceed residues values detected in 2005. While distribution of residues of  terbuthylazine according to soil layers relate with high sorption, higher content relate with higher persistence of herbicide.

Discusion

We can give reasons of fate of acetochlor and S-metolachlor in despite of negative finding in the soil. Negative findings of acetochlor relates with high presure of vapour. Acetochlor placement reduce losses by evaporation that is why we have a soft spot for mentioned way of application. Negative findings of S-metolachlor relates with high limit of detection and quantification  and with date of application. S-metolachlor was applied 14th April 2005, 24th April 2006 and 16th March 2007. It was applied about a month earlier than acetochlor, terbuthylazine and metribuzin and approximately two months earlier than dicamba in 2005. In 2006 was S-metolachlor applied one decade before metribuzin and almost two decades before terbuthylazine, acetochlor and dicamba, while in 2007 one month before acetochlor  and  one month and decade before terbuthylazine, dicamba and metribuzin application. 
Fate evaluation of dicamba, metribuzin and terbuthylazine is much difficult. Measured amounts of residues are indicative of  important role of chemical and physical soil properties as well as clear atmospheric exposure soon after the application, resp. influence of total weather conditions. Fate of herbicides e.g. terbuthylazine relates with content of clay minerals, organic matter and pH value (19). Our results confirm higher metribuzine and terbuthylazine residues level in the soil with higher content of clay particles and organic matter. Herbicide fixation provide protection from escape by runoff or leaching and microbial degradation as the main source of degradation. (9, 20, 21, 8, 10, 6 and many others). The herbicides metribuzin and terbuthylazine, either applied a month before dicamba at GF in 2005, were protect for escape during deluge by fixation, while dicamba manifest mobility. Lover content of terbuthylazine at EF in 2005 and lover till no content of metribuzin at GF and EF in 2005 till 2007 is probably result of higher activity of microorganisms, lower sorption capacity of sandy-loamy soil (medium hard), perhaps even result of  earlier term of application.
Dicamba residues were evidently distorted by deluge in 2005, while status in  2006 can be “normal”. Dicamba residues content in 2007 can be the result of earlier application and primarily result of the storm rainfalls in September followed by arid spring and summer. Dicamba was probably lost by leaching as water moves it down through soil macroporuses, soil cracks arose during long term dry season. Clay minerals bulking and shrinkage is the particularity of hard soils. We supposed that the soil cracks allowed preferential flow into the deeper soil layers as monitored layer 50 – 60 cm. We do not suppose favourable microbial degradation in the arid and hot weather conditions in 2007. According to Zhou et al. (22) the soil microbial activity is higher in the warmths and dampy soil with pH around neutral value. The values of hydrotermic coefficient explicitly show evidence of intensity of microbial activity and high degradation of herbicides at EF in 2005.
The most explicit results of the trial, not only in the case of dicamba were obtained from the valuation of soil layers. The relation between dicamba, metribuzin and terbuthylazine residues correlates with the herbicides mobility. We found that terbuthylazine was the most persistent. Despite expressive sorption potencial of terbuthylazine (19) it can be transported to the water reservoirs (23). Delphin and Chapot (24) present high horizontal variability of concentration of atrazine, metolachlor and diuron depending up on the depth of  herbicide placement in the soil solution of alluvial loamy soil. Herbicide placement together with cloddy strukture of top soil conduced to increase possibility of leakage. The heterogeneity was evaluate by the authors as the opportunity for water flow so there was a higher risk of ground water contamination. Standard deviation of herbicides residues content was influenced by mentioned heterogeneity. 
Different impact of tillage on dicamba, metribuzin  and terbuthylazine residues content in the soil interrelated with the herbicides mobility and intenzity of degradation (persistence). Intensity of herbicides leaching, resp. outflow depends on intensity and distribution of precipitation. Thete were different weather conditions during research period. It was found that weather attack is influenced by the tillage. Myers et al. (25) found that conventional tillage create conditions for smaller surface outflow, at once-and smaller herbicide leak as compared to no-till with and without postharvest remains of maize. It was found at water application rate 12.7 mm per hour and also at 50.8 mm per hour. The water was applicated 30 minutes after the use of herbicides atrazine and metolachlor. Lower values of outflow under conventional tillage generally resulted in higher concentrations of chemicals in the soil. According to tillage treatments the differences occured primarily in the soil layer 0 – 15 cm.
Our results, associated with dicamba at GF in 2005, indicates higher leaching at conventional tillage in comparison to reduced tillage and no-till. It was also found that the highest dicamba outlow at reduced tillage. Sume of precipitation after dicamba application at GF in 2005 was higher than water application rate simulated in experiment of Myers at al. (25). Our results corresponds to Gaynor et al. (26) conclusions in the study on herbicides with different mobility potencial (atrazine and metolachlor).  Authors found that no-till farming changed the sourse of mobility in compare with conventional tillage, but the major impact in term of herbicides losses had environmental factors after herbicides used. Plant residues are able to fix some herbicides. Dao (21) found that addition of straw increased organic carbon concentrations in the surface layers of soil at no-till and consequently retention of metribuzin increased two- to fivefold. According to Myers et al. (25) the highest concentrations of chemicals at conventional tillage as weel as notillage are in the soil layer 0 – 7.5 cm.  Authors also found that impact of tillage on herbicides concentrations was mainly in the soil layer 0 – 15 cm. Vertical leak out of dicamba throught the earthworm channels is higher  evently at notillage if it is raining one day after herbicides use and rain is intensive (38.6 mm 9th June 2005 at GF). Reduction of mentioned vertical leak at notillage at GF relate probably with one day delay of intensive rain. Vertical leak reduction was probably influenced also by low rain on the same day of herbicide use (0.7 mm 8th June 2005 at GF).
Finally the tillage systems influence on the degradation of herbicides. According to Gaston and Locke (27) the herbicides degradation is faster in the surface layers in compare with deeper layers of soil and is faster at conventional tillage in compare with notillage. In compliance with Hang et al (28) study of atrazine behaviour in the soil at no-till, only in a few isolated cases the faster herbicide degradation is in deeper soil layers than in the surface layers. Dao (20) found unbalanced degradation of metribuzin and S-ethylmetribuzin due to slow herbicide release fixated in the crop residues. Straw affinity is able to reduce efficiency of herbicides that were activated in the soil, if they were applied into soil surface at no-till. 

Conclusions

Our observations and results confirm the strong tillage impact on herbicide behaviour, that is affected by soil type, though determined by weather conditions. Dominant impact of weather affecting herbicides fate in step with environmental parameters of herbicides. Soil tillage as only one from observed factors may be used to manage the herbicides efficiency. Incorrect interaction of soil tillage and herbicide raise undesirable pollution of environment. According to the recent changes in soil tillage management is necessary to declare herbicides fate at environment in relation to tillage. 

References

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Abstract

The study compares the results of investigation of acetochlor (GC/MS), dicamba (HPLC/DAD), metribuzin (GC/ECD), S-metolachlor (GC/ECD) and terbuthylazine (GC/ECD) fate from topsoil (5-30 cm) and subsoil (50-60 cm) samples according to no-till technology (NT), reduced agrotechnique (RA) and conventional tillage (CT). The long-term stationary field trial was established on Gleyic Fluvisol (GF) and Eutric Fluvisol (EF) and valuated data come from the environmental conditions of 2005-2007, from Central European East Slovakian Lowland. All acetochlor and S-metolachlor residual analyses were negative findings, what is connected mainly with high vapour pressure or with high detection limit respectively. Dicamba, metribuzin and terbuthylazine residue content in soil was dependent on the used tillage system enhanced or delayed by soil conditions and actually determined by weathering. From herbicide own environmental fate parameters it was dominantly demonstrated the mobility concerning dicamba and sorption concerning terbuthylazine. However the greatest dicamba vertical movement was expected at NT when high-intensity rainfall occurred one day after it´s application concerning GF in 2005 invoking deluge event, the leaching was reduced by a delay in rainfall  and by low-intensity events prior to high intensity. Relations between dicamba residues content according agrotechnique variants indicate the source of escape altering, especially leaching and surface run-off  relevant for  CT and NT. In 2006 at normal weathering conditions there was higher dicamba content in  subsoil in comparing to topsoil, valid for each of three solved agrotechnique variants. Arid spring and summer conditions in 2007 formed soil cracks on heavy clay soil and subsequently humid September apparently resulted leaching at NT on GF. The higher metribuzin  and terbuthylazine content at GF corresponds to the herbicide own higher organic carbon sorption constant in one breath with higher sorption capacity of GF as EF.  In general there was the highest tebuthylazine residues conten on RA, less on CT and the least on NT.  

Keywords: tillage system, soil type, herbicide, residue

Contact address:

Ing. Štefan TÓTH, PhD., Ing. Martin DANILOVIČ, PhD., Slovak Centre of Agricultural Research – Institute of Agroecology, Michalovce, Špitalska 1273, 071 01 Michalovce, Slovak Republic, e-mail: toth@minet.sk